Semiconductor device

ABSTRACT

A semiconductor device includes an electrically conductive III-V doped semiconductor substrate of a first conduction type, a photodiode array having photodiode structures disposed on the III-V doped semiconductor substrate, a first III-V doped semiconductor layer of a second conduction type disposed between the photodiode structures and the III-V doped semiconductor substrate, etching trenches disposed on the III-V doped semiconductor substrate, each of the trenches having inner sides, the inner sides having an insulation layer and a metallization layer for electrically connecting the photodiode structures in series, the metallization layer disposed on the insulation layer, and partition lines separating each of the photodiode structures from others of the photodiode structures for producing an individual photodiode structure when the array is cut through the first III-V doped semiconductor layer along the partition lines.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a division of U.S. application Ser. No. 08/940,600, filedSep. 29, 1997.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a semiconductor device, in which atleast one functional semiconductor structure is assigned to a first mainsurface of a III-V semiconductor substrate, and in which the functionalsemiconductor structure is electrically insulated from a second mainsurface of the III-V semiconductor substrate which is opposite the firstmain surface.

[0004] A semiconductor device of this type is, for example, disclosed byFranklin S. Harris, Jr., Applied Optics, Vol. 27, No. 15, page 3141.That article describes a photodiode array in which a multiplicity ofAlGaAs/GaAs photodiodes are monolithically integrated on a so-calledsemi-insulating GaAs substrate.

[0005] In addition, G. Müller, M. Honsberg, Journal of OpticalCommunications 6 (1985), June No. 2, Berlin, Germany, page 42, disclosesa MCRW laser structure which is applied to a semi-insulating GaAssubstrate. The semi-insulating GaAs substrate is used to electricallyinsulate a plurality of monolithic integrated components from oneanother on the substrate.

[0006] The insulating affect of semi-insulating substrates is achievedby incorporating low impurity levels into the substrates (for example Cror C in the case of GaAs substrates, and Fe in the case of InPsubstrates). However, the incorporation of dopants of this type into aIII-V crystal lattice entails a number of difficulties both in theproduction and in the handling of the lattice. It is thus, for example,very difficult to incorporate these dopants uniformly into the III-Vcrystal lattice and makes it considerably more difficult to produce auniform insulation affect over the entire surface of a semi-insulatingsubstrate. The production yield of semiconductor components havingsemi-insulating substrates is therefore very low, for example, incomparison with the production of semiconductor components on conductiveGaAs substrates.

[0007] A further problem with the semi-insulating semiconductorsubstrates is the fact that their insulation effect is drasticallyreduced when experiencing a moderate increase in temperature becausefree charge carriers are produced in the semiconductor crystal.

SUMMARY OF THE INVENTION

[0008] It is accordingly an object of the invention to provide asemiconductor device which overcomes the herein-mentioned disadvantagesof the heretofore-known devices, and which provides homogenouselectrical insulation properties between the functional semiconductorstructure disposed above the first main surface of a III-V semiconductorsubstrate and the second main surface of the III-V semiconductorsubstrate and which also provides an effective electrical insulationeffect at high operating temperatures.

[0009] With the foregoing and other objects in view there is provided,in accordance with the invention, a semiconductor device, comprising anelectrically conductive III-V semiconductor substrate having mutuallyopposite first and second main surfaces; at least one pn junction,reverse biased during operation of the semiconductor device, anddisposed above the first main surface; and at least one functionalsemiconductor structure disposed above the at least one pn junction, thefunctional semiconductor structure being electrically insulated from thesecond main surface of the III-V semiconductor substrate.

[0010] According to the invention an electrically conductive III-Vsemiconductor substrate is provided and at least one pn junction,reverse biased during operation of the semiconductor device, is disposedbetween the functional semiconductor structure and the III-Vsemiconductor substrate. That has, in particular, the advantage ofproviding a conductive substrate which is substantially easier toproduce and therefore more cost effective than prior art semi-insulatingsubstrates which require a more elaborate production process. The pnjunction which is reverse biased during operation undertakes theelectrical insulation of the functional semiconductor structure from thesecond main surface of the III-V semiconductor substrate.

[0011] In accordance with an added feature of the invention, theelectrically conductive III-V semiconductor substrate has a chargecarrier concentration of more than 1*10¹⁵ cm−3 at room temperature.

[0012] In accordance with another feature of the invention, theelectrically conductive III-V semiconductor substrate has a chargecarrier concentration of between 1*10¹⁶ cm⁻³ and 1*10¹⁹ cm⁻³ at roomtemperature.

[0013] In a preferred embodiment of the semiconductor device accordingto the invention, the electrically conductive III-V semiconductorsubstrate has a charge carrier concentration of >1·10¹⁵ is cm⁻³ at roomtemperature (that is to say at about 20° C.). It is particularlyadvantageous if the electrically conductive III-V semiconductorsubstrate has a charge carrier concentration of between 1·10¹⁶ cm⁻³ and1·10¹⁹ cm⁻³ at room temperature. III-V semiconductor substrates of thistype are produced in large numbers for conventional III-V semiconductorcomponents and are therefore available at low cost.

[0014] In accordance with an addition feature of the invention, theIII-V semiconductor substrate has a first conduction type, and includesa first doped III-V semiconductor layer of a second conduction typedisposed between the III-V semiconductor substrate of the firstconduction type and the at least one functional semiconductor structure.In accordance with yet another added feature of the invention, there isa second doped III-V semiconductor layer of the first conduction typedisposed between the at least one functional semiconductor layer and thefirst doped III-V semiconductor layer in such a way that the III-Vsemiconductor substrate, the first doped II-V semiconductor layer andthe second doped III-V semiconductor layers form the at least one pnjunction disposed in opposite directions.

[0015] In an advantageous configuration of the semiconductor deviceaccording to the invention, a doped III-V semiconductor substrate of afirst conduction type is provided. Applied to that is a first dopedIII-V semiconductor layer of a second conduction type, to which a seconddoped III-V semiconductor layer of the first conduction type is in turnapplied. The functional semiconductor structure is arranged on thesecond doped III-V semiconductor layer. The III-V semiconductorsubstrate and the first and the second doped III-V semiconductor layerstogether form two pn junctions of opposite directions. With a layersequence of this type, one of the two pn junctions is always reversebiased during operation, irrespective of the conduction type possessedby a semiconductor layer of the functional semiconductor structureapplied to the second doped III-V semiconductor layer.

[0016] In yet another additional feature of the invention, the at leastone functional semiconductor structure is an MCRW laser structure.

[0017] In accordance with yet another feature of the invention, thereare photodiode structures having a photodiode array disposed on the atleast one functional semiconductor structure.

[0018] In accordance with yet another added feature of the invention,the at least one functional semiconductor structures are at least twomonolithically integrated functional semiconductor structures, and theat least one pn junction is disposed between each of the at least twomonolithically functional semiconductor structures and the second mainsurface of the electrically conductive III-V semiconductor substrate.

[0019] In accordance with yet another additional feature of theinvention, the at least one pn junction is cut in an intermediatelocation between two of the at least two monolithically integratedfunctional semiconductor structures in such a way that there is noconductive electrical connection between the at least two monolithicallyintegrated functional semiconductor structures via the III-Vsemiconductor substrate and inclusive of at least one of the first dopedIII-V semiconductor layer and the second doped III-V semiconductorlayer.

[0020] In accordance with a concomitant feature of the invention, the atleast one functional semiconductor structure is at least two monolithicintegrated functional semiconductor structures of different types.

[0021] With the objects of the invention in view, there is also provideda semiconductor device, including an electrically conductive Ill-V dopedsemiconductor substrate of a first conduction type, a photodiode arrayhaving photodiode structures disposed on the III-V doped semiconductorsubstrate, a first III-V doped semiconductor layer of a secondconduction type disposed between the photodiode structures and the Ill-Vdoped semiconductor substrate, etching trenches disposed on the III-Vdoped semiconductor substrate, each of the trenches having inner sides,the inner sides having an insulation layer and a metallization layer forelectrically connecting the photodiode structures in series, themetallization layer disposed on the insulation layer, and partitionlines separating each of the photodiode structures from others of thephotodiode structures for producing an individual photodiode structurewhen the array is cut through the first III-V doped semiconductor layeralong the partition lines.

[0022] In a further embodiment of the semiconductor device according tothe invention, at least two monolithic integrated functionalsemiconductor structures are assigned to the electrically conductiveIII-V semiconductor substrate, and at least one pn junction which isreverse biased during operation of the semiconductor device is arrangedbetween each of the functional semiconductor structures and theelectrically conductive III-V semiconductor substrate. The pn junction,or the pn junctions is or are cut in an intermediate space between thefunctional semiconductor structures in such a way that there is noconductive electrical connection between the functional semiconductorstructures via the III-V semiconductor substrate, where appropriateinclusive of one or more III-V semiconductor layers applied thereto.That is the case whenever the current path between two functionalsemiconductor structures would lead via a reverse biased pn junction.With a semiconductor device of this type, it is possible to produce insimple fashion an integrated circuit configuration of a multiplicity ofIII-V semiconductor components on a single III-V semiconductorsubstrate.

[0023] With the foregoing and other objects in view there is alsoprovided, in accordance with the invention, a process for producing asemiconductor device, which comprises: a) producing a doped III-Vsemiconductor substrate of a first conduction type; b) applying a firstdoped III-V semiconductor layer of a second conduction type to the III-Vsemiconductor substrate; c) applying a second doped III-V semiconductorlayer of the first conduction type to the first doped III-Vsemiconductor layer; d) applying an active layer system to the seconddoped III-V semiconductor layer; and e) producing at least twofunctional semiconductor structures electrically insulated from oneanother, by cutting the active layer system inclusive of the first andthe second doped III-V semiconductor layers.

[0024] In a preferred process for producing a semiconductor deviceaccording to the invention, a first doped III-V semiconductor layer ofthe second conduction type is applied to a prefabricated doped III-Vsemiconductor substrate of the first conduction type. An active layersystem of at least one functional semiconductor structure is thenapplied to the first doped III-V semiconductor layer or to a seconddoped III-V semiconductor layer of the first conduction type which isadditionally applied to the first doped III-V semiconductor layer. Afterthat, by cutting (for example etching through or sawing) the activelayer system, inclusive of the first and, if appropriate, the seconddoped III-V semiconductor layers, at least two functional semiconductorstructures are produced which are electrically insulated from oneanother. These can then be electrically connected to one another byproviding contact metalizations and, if appropriate, be connected tofurther components arranged externally.

[0025] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0026] Although the invention is illustrated and described herein asembodied in semiconductor device, it is nevertheless not intended to belimited to the details shown, since various modifications and structuralchanges may be made therein without departing from the spirit of theinvention and within the scope and range of equivalents of the claims.

[0027] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a diagrammatic, cross-sectional view of a firstembodiment of the semiconductor device according to the invention; and

[0029]FIG. 2 is a diagrammatic, cross-sectional view of a secondembodiment of a semiconductor device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Referring now to the figures of the drawing in detail and first,particularly, to FIG. 1 thereof, there is shown a functionalsemiconductor structure 1 which is an MCRW laser structure 9. Thefunctional semiconductor structure 1 is applied to a layer sequencewhich is formed of a III-V semiconductor substrate 3. Applied to theIII-V semiconductor substrate 3 is a first doped III-V semiconductorlayer 6 to which a second doped III-V semiconductor layer 7 is in turnapplied. The III-V semiconductor substrate 3 is, for example, producedfrom n doped GaAs, and the first 6 and second 7 doped III-Vsemiconductor layers are formed, for example, of p doped or n dopedGaAs. The III-V semiconductor substrate 3 and the first 6 and second 7doped III-V semiconductor layers form two pn junctions 4, 5 facing inopposite directions. A metalization layer 13 is applied to the secondmain surface 12 opposite a first main surface 11 of the III-Vsemiconductor substrate 3. The metalization layer, for example, can beformed of Cr/In. The metalization layer is, for example, used forsoldering the semiconductor device to a heat sink made of copper. Thedopants used for the III-V semiconductor substrate 3 and the first 6 andsecond 7 doped III-V semiconductor layers are, for example, the dopantscustomarily used in semiconductor technology for III-V semiconductormaterials. These dopants will therefore not be explained in furtherdetail at this point.

[0031] The functional semiconductor structure 1 of the MCRW laserstructure 9 is applied to the second doped III-V semiconductor layer 7,for example by MOVPE or MBE. The functional semiconductor structure 1,for example, is formed of an n⁺ doped GaAs layer 14, an n doped GaAlAslayer 15, an active layer 16 of undoped GaAs or of an active layersequence/system, a p doped GaAlAs layer 17 and a p⁺ doped GaAs layer 18.The n⁺ doped GaAs layer 14 is, for example, provided with an n contact19, formed of AuGe/Ni/Au, and the p doped GaAlAs layer 17 as well as then⁺ doped GaAs layer 18 are provided with a p contact metalization 20which is formed of for example by Cr/Au, Cr/Pt/Au, Ti/Pt/Au or Ti/Aulayer sequence. That is a usual MCRW laser structure, known to theperson skilled in the art, which therefore needs no further explanationat this point.

[0032] Clearly, a plurality of MCRW laser structures 9, which areelectrically insulated from one another, may be formed on the III-Vsemiconductor substrate 3 having the first 6 and the second 7 dopedIII-V semiconductor layer according to the first illustrativeembodiment. The structure shows that the electrical insulation isprovided through the substrate. The individual MCRW laser structures maynaturally be connected with one another via metalization tracks.

[0033]FIG. 2 represents an illustrative embodiment of a semiconductordevice according to the invention, in which a multiplicity of photodiodestructures 10 of a photodiode array 8 are applied to a singleelectrically conductive III-V semiconductor substrate 3 of the firstconduction type. The first doped III-V semiconductor layer 6 of thesecond conduction type is in each case arranged between the photodiodestructures 10 and the electrically conductive III-V semiconductorsubstrate 3 which, for example, can be formed of n doped GaAS. Thesemiconductor layer, for example, can be formed of p doped GaAs.Starting from the first doped III-V semiconductor layer 6, thephotodiode structures 10 are in each case composed of an n doped GaAslayer 21, a p doped GaAs layer 22 and a p doped AlGaAs layer 23. Theindividual photodiode structures 10 are produced by cutting this layersequence into multiple parts, inclusive of the first doped III-Vsemiconductor layer 6, along predetermined partition lines, for example,by the use of etching trenches 24. The insides of the etching trenches24 are provided with an insulation layer 25, for example, an insulationlayer of SiO₂, to which a metalization layer 26 via which the individualphotodiode structures 10 are connected serially with one another isapplied.

[0034] The semiconductor device is again a customary semiconductorcomponent known to the person skilled in the art, and will therefore notbe explained in further detail at this point.

[0035] Clearly, any other type of III-V semiconductor material may beused in the semiconductor device according to the invention instead ofthe GaAs III-V semiconductor substrate 3 mentioned in the illustrativeembodiments. The choice of the type of III-V semiconductor material isdependent on the type of functional semiconductor structure that isapplied to the substrate. Likewise, it may naturally also be configuredas p conductive. The first and the second doped III-V semiconductorlayers should then be matched accordingly.

[0036] One advantage of conductive III-V semiconductor substrates oversemi-insulating substrates is that the crystal growth process issubstantially easier to control. That leads to more uniform wafers whosedopant (generally Si) is further distinguished by little diffusioneffects.

[0037] In addition, the dopants for the pn junction or junctions mayadvantageously be incorporated into the III-V crystal latticeepitaxially, for example by the utilization of MOVPE or MBE, as a resultof which a higher quality in comparison with the substrate (lowerimpurity concentration, lower dislocation densities, etc.) and thereforea substantially better thermal stability are achieved.

[0038] Of course, the invention also provides for the arrangement ofdifferent types of functional semiconductor structures 1, for examplephotodiodes, light-emitting diodes, transistors, MCRW laser diodes,etc., on the same electrically conductive III-V semiconductor substrate3.

I claim:
 1. A semiconductor device, comprising: an electricallyconductive Ill-V doped semiconductor substrate of a first conductiontype; a photodiode array having photodiode structures disposed on saidIII-V doped semiconductor substrate; a first III-V doped semiconductorlayer of a second conduction type disposed between said photodiodestructures and said III-V doped semiconductor substrate; etchingtrenches disposed on said III-V doped semiconductor substrate, each ofsaid trenches having inner sides, said inner sides having an insulationlayer and a metallization layer for electrically connecting saidphotodiode structures in series, said metallization layer disposed onsaid insulation layer; and partition lines separating each of saidphotodiode structures from others of said photodiode structures forproducing an individual photodiode structure when said array is cutthrough said first III-V doped semiconductor layer along said partitionlines.
 2. The semiconductor device according to claim 1 , wherein saidIII-V doped semiconductor substrate has a charge carrier concentrationof more than 1*10¹⁵ cm⁻³ at room temperature.
 3. The semiconductordevice according to claim 2 , wherein said III-V doped semiconductorsubstrate has a charge carrier concentration of between 1*10¹⁶ cm⁻³ and1*10¹⁹ cm⁻³ at room temperature.
 4. The semiconductor device accordingto claim 1 , wherein said photodiode structures include a metal cladridge waveguide laser structure.
 5. The semiconductor device accordingto claim 1 , wherein said photodiode structures include at least twomonolithic integrated functional semiconductor structures of differenttypes.
 6. The semiconductor device according to claim 1 , wherein saidetching trenches are disposed between each of said photodiodestructures.